1. Field of the Invention
The present invention relates to a charging-roller bearing member, process cartridge, and image forming apparatus for use in an image forming apparatus to be used as electrophotography-applied output recording equipment, such as a copier, printer, or facsimile.
2. Description of the Related Art
In an image forming apparatus, such as a copier, printer, facsimile machine, or printing machine, a process cartridge may be used having accommodated therein at least one of a charging unit, a developing unit, and a cleaning unit among a latent image carrier and devices for an image forming process. Such a process cartridge is removably provided to an image forming apparatus body. By taking the process cartridge outside of the apparatus at the time of replacement and maintenance inspection, the work in a narrow space within the apparatus is reduced. Also, such a configuration of the process cartridge has been known in which, for example, a photosensitive drum, which is a drum-shaped latent image carrier, is rotatably supported in a casing forming the cartridge and a charging roller that performs a charging process onto this photosensitive drum is mounted inside the casing.
Japanese Patent Application Laid-Open No. 2002-214885 (hereinafter, “first patent document”) discloses a configuration, as a supporting configuration for the charging roller, in which both ends of a rotating shaft of the charging roller in an axial direction are supported via a bearing by both side walls of the casing of the cartridge.
However, as disclosed in the first patent document, when both of the photosensitive drum and the charging unit that performs a charging process, which is an image forming process onto the photosensitive drum, are incorporated in the casing forming the process cartridge, the following problems may occur depending on the supporting configuration of the photosensitive drum.
When the photosensitive drum is used to form not only a single image but also a multi-color image, such as a full-color image, optimization of a starting position for writing an electrostatic latent image of each photosensitive drum forming each color image is critical in preventing an image color shift and density unevenness.
To achieve this, in a configuration for matching write starting positions of the photosensitive drums in a main scanning direction, positional regulation may be performed in an axial direction in parallel with the main scanning direction of the photosensitive drum.
In an example of the configuration, a flange is disposed between a inner side wall of the cartridge and an end face of the photosensitive drum on one side in an axial direction of the photosensitive drum accommodated in the process cartridge, thereby regulating the position in an axial direction, that is, a so-called thrust direction. Also, a gear is formed on an outer perimeter surface of the flange for shared use as a driving-force transmitting unit.
The charging roller is configured in a manner such that both ends in an axial direction are supported with reference to the same center in the axial direction as the center in the axial direction of the photosensitive drum. Thus, in a supporting configuration for the photosensitive drum and the charging roller incorporated in the process cartridge, in the case of the photosensitive drum, for example, both ends thereof in an axial direction are supported by side walls of the casing of the process cartridge so that the length in an axial direction is longer than that of the charging roller with provision of the gear-added flange. On the other hand, since the charging roller has a length in an axial direction enough to cover the length of an image forming area on the photosensitive drum, the charging roller is located in a range shorter than the axial length of the photosensitive drum. For this reason, both ends of the charging roller in an axial direction are supported not by the side walls of the casing but by, for example, supporting brackets newly provided between the side walls of the casing.
In such a supporting configuration for the charging roller, a space on a side where the gear-added flange on a photosensitive drum side is not present is present as a waste portion. Accordingly, with such a superfluous space in an axial direction of the charging roller occupying the inside of the process cartridge, the process cartridge may be disadvantageously upsized. Moreover, the supporting brackets for supporting both ends of the charging roller in an axial direction are provided between the walls inside the casing, thereby not only upsizing the configuration but also degrading workability because an operation of assembling the charging roller is performed within the inner side walls of the casing, which is a limited narrow space. In particular, since the charging roller is a power-supply member, it is important to ensure a power-supply path. However, in the case of a configuration with wiring between the side walls of the casing, not only a wiring operation but also maintenance workability tends to deteriorate.